The use of adaptive power allocation with adaptive modulation/coding to allow flexibility in modifying power allocation has been of increasing interest both in the fixed wireless and cellular world.
In systems with power control capability, the power of a transmitted signal can be adjusted in order to meet a target signal quality, such as signal to interference ratio (“SIR”) or signal to noise ratio (“SNR”) or signal to interference plus noise ratio (“SINR”), at the receiver. In such a system, the transmit power will typically be low when a user is close to a base station and will increase with distance from the base station. However, with such applications, a compromise is made between coverage reliability and system capacity. If the system uses a robust form of modulation, such as Binary Phase Shift Keying (B-PSK), good coverage reliability can be obtained, but the system capacity and data rate may be lower than is desired. If, in an attempt to increase data rate and capacity, the system uses a more aggressive form of modulation, such as 8-PSK, the higher SINR requirement cannot be met for all of the users. As a result coverage reliability may be significantly reduced.
Accordingly, various methods were proposed in the past in the attempt to address the problem of implementing adaptive power allocation which achieve relatively high system capacity and system coverage, which provide adaptive modulation/coding capabilities and which provide flexibility to dynamically modify the adaptive power allocation.
U.S. Pat. No. 6,625,776 describes an adaptive coding scheme for controlling, independently, transmit power and coding levels for data transmitted in uplinks and downlinks by determining a data error rate associated with downlink data (e.g., a character error rate provided by a Reed Solomon decoder). This way, the level of coding (e.g., heavy or light) on data in the downlink to meet a desired data error rate, can be achieved.
U.S. Pat. No. 6,690,652 discloses an adaptive power control in wideband CDMA cellular systems (WCDMA) that is achieved by transmitting control signals between the BS and a mobile station to reconfigure their transmitter/receiver. Reconfiguration is performed according to the prediction of the channel attenuation and the threshold set at the BS or mobile station based on its channel power probability density function.
U.S. Pat. No. 6,216,010 describes an up-link power control for fixed wireless access communication networks. The distance information between an outstation and a base station and information relating to channel loss is employed by a power control algorithm whereby the signal power transmitted can be optimally controlled. This publication provides a power control strategy which adapts to the total channel loss as well as to the components of this loss.
U.S. Pat. No. 5,978,414 relates to a method for determining a transmission rate for encoded data frame, which relies on decoding signal at each candidate rate and using decoding reliability parameter or comparison with input, to identify one or more candidate transmission rates based upon the decoding reliability parameters. If there is only one candidate transmission rate, the actual transmission rate is determined to be that candidate transmission rate. If there is more than one candidate transmission rate, the decoded signals are re-encoded at the candidate transmission rates at which they were decoded. The bits of the communication are then compared with the bits of the re-encoded signals for each candidate transmission rate to determine the actual transmission rate.
U.S. Pat. No. 6,385,462 describes a method for providing criterion based adaptive power allocation with selective determination of modulation and coding. The method comprises providing adaptive power allocation with a target signal quality for each link based on a system criterion, and a modulation/coding rate for each link based on the signal quality associated with the transmit power of each link.
U.S. Pat. No. 6,683,916 discloses a method for adaptive modulation/coding and power allocation by reducing excess power for one data stream while retaining the same encoding rate, and increasing power level of another while increasing its encoding rate.
One of the methods known in the art for simulating link-system interface by estimating the demodulator performance in selective channel is the Exponential Effective SIR Mapping (“EESM”). The EESM estimates the effective SINR through the use of the following formula:
      γ    eff    ≡      EESM    ⁡          (              γ        ,        β            )        ≡            -      β        ·          ln      ⁡              (                              1            N                    ·                                    ∑                              i                =                1                            N                        ⁢                          ⅇ                              -                                                      γ                    i                                    β                                                                    )            where:                γ is the a vector [γ1γ2, . . . ,γN] of the per OFDM tone SINRs, which are typically different in a selective channel;        γeff is the effective SINR;        γi is the SINR of the i-th subcarrier, or segment in which channel response remains approximately constant;        β is the adjustment factor necessary for QPSK or higher-order modulation scheme; and        N is the total number of subcarriers, or segments that have approximately constant channel response.        
According to A. Tee et al., in “Link-System Interface Simulation Methodologies” published on Jun. 29, 2004, simulation data has indicated that the same factor β may be used for different channel models with the same modulation and coding scheme.
Each of the references mentioned is hereby incorporated by reference as if fully set forth herein.